RISSOA. 41 



6, convex, loosely and obliquely coiled, the last three being 

 nearly eqnal in breadth, and the first minute ; the body-whorl 

 occupies nearly two-thirds of the spire : suture remarkably 

 deep : mouth exactly oval, small, and slightly expanding : outer 

 lip thin, contracted, and incurved above : inner lip somewhat 

 reflected, and more or less detached from the pillar : operculum 

 few-whorled, light-horncolour, with the spire placed excen- 

 trically. L. 0-135. B. 0-05. 



Habitat : Mud in the coralline zone, Dorset, Devon, 

 Cornwall, Bristol and English Channels ; Northumber- 

 land coast (Alder) ; south and west of Ireland and Dub- 

 lin Bay; Dunbar (Bingham, fide Brown) ; Moray Firth 

 (Macgillivray and Macdonald) ; west coast of Scotland 

 (Barlee and J. G. J.) ; Orkneys (Thomas) ; and Bressay 

 in Shetland (Fleming) . It is local and somewhat rare. 

 Fossil in the Coralline Crag at Sutton (Wood). Pro- 

 fessor Sars has dredged it of a very large size off Floroen 

 in Finmark; Malm obtained forty-five specimens, of 

 which several were living, in 20-30 f. on the Bohuslan 

 coast ; La Hogue Bay near Cherbourg (Mace) ; Vigo 

 (M 'Andrew) ; Gulf of Lyons, in the stomach of As- 

 tropecten irregularis, with R. proximo, (Martin) ; Spezzia 

 (J. G. J.). 



Very active, and suspends itself by a single byssal 

 thread, keeping the mouth of the shell closed by the 

 operculum. 



Captain Brown made of this species three, which 

 he called vitrea, crystallina, and virginea. A shell kindly 

 given me by M. Nyst, from the Belgian tertiaries, as 

 R. vitrea, is twice as large as our shell ; it has an angu- 

 lated periphery, a shallower and straight suture, fewer 

 though more conspicuous spiral striae, and an acute- 

 angled outer lip, the inner lip being closely attached 

 throughout to the pillar. 



